To elongate base material ingot for optical fibers to make a base material rod for optical fibers having a smaller diameter, the method in which while the base material ingot is set and heated to be softened in an air-through vertical electric furnace, the ingot is fed from the entrance of the electric furnace at a certain speed, grasped the fore-end thereof and drawn at a higher speed than the feed speed so that the base material rod having a smaller diameter than the base material ingot can be drawn has been disclosed in Patent Document 1.
Patent Document 1: Japanese Patent Application Publication No. 62-167236.